U.S. patent number 4,807,278 [Application Number 07/048,736] was granted by the patent office on 1989-02-21 for telecommunication controller having a telephone line sharing function.
Invention is credited to David W. Ross.
United States Patent |
4,807,278 |
Ross |
February 21, 1989 |
**Please see images for:
( Certificate of Correction ) ** |
Telecommunication controller having a telephone line sharing
function
Abstract
A control system has two switches for connecting a telephone
device and a data device to a common telephone line. Separate
circuits are provided to sense the current flowing between the
telephone line and each of the devices. The circuits are coupled to
the switches so that when the sensed current for one of the devices
exceeds a given level, the switch for the other device is activated
to disconnect the other device from the telephone line.
Inventors: |
Ross; David W. (West Allis,
WI) |
Family
ID: |
21956179 |
Appl.
No.: |
07/048,736 |
Filed: |
May 11, 1987 |
Current U.S.
Class: |
379/184; 379/194;
379/93.09 |
Current CPC
Class: |
H04M
1/70 (20130101); H04M 11/06 (20130101) |
Current International
Class: |
H04M
1/70 (20060101); H04M 1/68 (20060101); H04M
11/06 (20060101); H04M 001/70 (); H04M
011/00 () |
Field of
Search: |
;379/93,95,96,97,98,161,184,194,195,208,442,443,106,107,168,377,379 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: George; Keith E.
Attorney, Agent or Firm: Quarles & Brady
Claims
I claim:
1. An apparatus for coupling a plurality of telephone line
utilizing devices to a shared telephone line comprising:
a plurality of electrically operable switches, each of which
couples one of the utilizing devices to the shared telephone
line;
a plurality of electric current sensing means, each having means
for producing an output voltage which corresponds to the level of
current flowing between the telephone line and a different one of
the utilizing devices, a voltage comparator for comparing the
output voltage to a reference voltage, and a capacitor and a
resistor coupled in parallel between an input of said voltage
comparator and substantially ground potential to inhibit a ringing
signal on the telephone line from activating said switches; and
means, responsive to the voltage comparators of said plurality of
current sensing means, for activating said switches to disconnect
the other utilizing devices from the telephone line when the
current flowing between the telephone line and one of the utilizing
devices exceeds a given level.
2. The apparatus as recited in claim 2 wherein each of the means
for producing an output voltage includes an opto-isolator.
3. The apparatus as recited in claim 1 wherein each of said current
sensing means is coupled to the telephone line by a bridge
rectifier.
4. An apparatus for coupling first and second utilizing devices to
a telephone line comprising:
a voltage supply means separate from the telephone line;
a first switch coupling the first utilizing device to the telephone
line;
a second switch coupling the second utilizing device to the
telephone line;
a first rectifier bridge having one alternating current terminal
coupled to the telephone line, another alternating current terminal
coupled to the first utilizing device, and two direct current
terminals;
a first opto-isolator coupled to the direct current terminals of
said first bridge rectifier and coupled to the voltage supply means
to produce an output voltage representative of the level of current
flowing between the telephone line and the first utilizing
device;
a first voltage comparator for comparing the output voltage from
the first opto-isolator to a reference voltage level;
first means, responsive to an output signal from the first voltage
comparator, for activating said second switch to disconnect the
second utilizing device from the telephone line;
a first means, connected to an input of said first voltage
comparator, for preventing a ringing signal on the telephone line
from causing said first voltage comparator to produce an output
signal which activates said second switch;
a second rectifier bridge having one alternating current terminal
coupled to the telephone line, another alternating current terminal
coupled to the second utilizing device, and two direct current
terminals;
a second opto-isolator coupled to the direct current terminals of
said second bridge rectifier and coupled to the voltage supply
means to produce an output voltage representative of the level of
current flowing between the telephone line and the second utilizing
device;
a second voltage comparator for comparing the output voltage from
the second opto-isolator to a reference voltage level;
second means, responsive to an output signal from the second
voltage comparator, for activating said first switch to disconnect
the first utilizing device from the telephone line; and
a second means, connected to an input of said second voltage
comparator, for preventing a ringing signal on the telephone line
form causing said second voltage comparator to produce an output
signal which activates said first switch.
5. The apparatus as recited in claim 4 further comprising a
separate rectifier means coupled across the direct current
terminals of each of the first and second rectifier bridges.
6. The apparatus as recited in claim 4 wherein
said first means for preventing includes a first resistor and a
first capacitor coupled to an input of said first voltage
comparator and having an RC time constant which prevents the
ringing signal from causing said first comparator to produce the
output signal to which said first means for activating responds;
and
said second means for preventing includes a second resistor and a
second capacitor coupled to an input of said second voltage
comparator and having an RC time constant which prevents the
ringing signal from causing said second comparator to produce the
output signal to which said second means for activating
responds.
7. The apparatus as recited in claim 4 wherein
said first means for preventing includes a first resistor coupled
between an input of said first voltage comparator and ground, and
first capacitor coupled between the input of said first voltage
comparator and ground; and
said second means for preventing includes a second resistor coupled
between an input of the second voltage comparator and ground, and a
second capacitor coupled between the input of the second voltage
comparator and ground.
Description
The present invention relates to the sharing of a telephone line by
a telephone system and a computer data communication device.
BACKGROUND OF THE INVENTION
With increasing frequency, telephone lines are being used in
conjunction with data devices for data communication. Typical data
devices in this discussion include computer modems, facsimile
machines and any other data equipment which are capable of
communicating over a standard two-wire telephone line.
Costs involved in maintaining separate telephone lines for voice
and data make it desirable to share a telephone line with both a
telephone system, such as a telephone instrument, and a data
device. However, problems often result from connecting a data
device and a telephone instrument directly to the same telephone
line. The most common problem occurs when a data device is using a
telephone line to communicate with another similar distant data
device, and a telephone instrument on the same telephone line is
picked up. The electrical noise generated on the telephone line by
the connection of the telephone instrument causes data flow errors
between the data devices. The operators of the data equipment may
then be required to reset the data devices and restart the data
transmissions.
It is, therefore, desirable to have a line control device which
will allow only a telephone system or a data device to operate on
the same telephone line at one time. This will prevent data flow
errors on the telephone line between data devices resulting from
the connection and use of a telephone system on that same telephone
line.
There are many variations in the electrical characteristics of the
telephone circuits, data devices and telephone systems. Typical
variations in telephone circuits include (1) an open circuit
operating voltage of the telephone line between 15 and 52 volts
direct current, (2) a loop resistance of the telephone line between
500 and 4000 ohms and (3) an active, or off-hook, resistance of the
telephone system and the data device between 30 and 500 ohms. The
control device used must also be able to pass, yet be insensitive
to, the high voltage ringing current, usually between 75 and 120
volts alternating current at 16 to 75 hertz. For an automatic line
control device to properly detect the active state of a data device
or a telephone system on a shared telephone line, the control
device must be able to operate over these wide variations of
electrical characteristics. The wider the range of electrical
variations over which the device can operate, the more universal
the compatability of the control device with different telephone
lines, data devices and telephone systems.
SUMMARY OF THE INVENTION
An automatic telephone line control device has a pair of connectors
to which a standard two wire telephone line may be connected. Two
pairs of output connectors are provided to connect two telephone
line using apparatus to the control device. Each of the pairs of
output connectors is coupled to the connectors for the telephone
line by a separate electrically operable switch.
A separate current sensing circuit is coupled to each pair of
output connectors to sense the current flowing through at least one
of the connectors of each pair. When the current through one of the
pairs of output connectors rises above a given level, the sensing
circuit sends a signal to the electrically operable switch for the
other pair. This signal causes the switch to disconnect the other
pair of output connectors from the telephone line connectors.
An object of the present invention is to provide a telephone line
control circuit which allows a data device and a telephone system
to have equal access to a common telephone line.
Another object is to enable the control circuit to provide such
equal access while allowing only the data device or telephone
system to operate on the telephone line at any given time.
Another object of the present invention is to allow two apparatus
to share access to a common telephone line without one apparatus
interfering with the communications by the other apparatus.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE of the drawing is a schematic diagram of the present
telephone line control circuit.
DETAILED DESCRIPTION OF THE INVENTION
With reference to the FIGURE, an automatic telecommunication
control circuit 100 has first and second system power terminals 101
and 102 to which 12 volt direct current system power is applied.
The first system power terminal 101 is connected to system ground,
which is not the same as earth ground. The second power terminal
102 serves as a positive voltage source for the circuit
components.
The incoming telephone line tip conductor and the ring conductor
are connected to telephone line connectors 103 and 104. The
telephone line tip connector 103 is coupled to a terminal of a
first switch pole 106 of a first DPST relay K1 and to a terminal of
a first switch pole 107 of a second DPST relay K2. Another terminal
of the first switch pole 106 of relay K1 s coupled to a telephone
system tip connector 111. Another terminal of the first pole 107 of
the second relay K2 connects to a data device tip connector 132.
The telephone line ring connector 104 is coupled to a terminal of a
second switch pole 109 of the first relay K1 and to a terminal of a
second switch pole 110 of the second relay K2.
The ring connectors for the telephone system and the data device
112 and 133 respectively, are coupled to two current sensing
circuits which detect whether the telephone system or the data
device is using the telephone line. Both sensing circuits are
identical. As used herein the telephone system may be a single
telephone instrument, a PABX, or similar equipment.
For the telephone sensor circuit, the telephone system ring
connector 112 is connected to the negative terminal of a first
electrolytic capacitor C1 and to the one alternating current input
of a bridge rectifier IC3. The other alternating current input of
bridge rectifier IC3 is connected to the positive terminal of first
electrolytic capacitor C1 and to another terminal of the second
switch pole 109 of the first relay K1.
The positive output terminal of bridge rectifier IC3 connects to
node 117 and its negative output terminal is connected to node 118.
Three diodes D1, D2 and D3 are connected in a forward biased series
between nodes 117 and 118 to form a voltage clamping mechanism. A
first resistor R1 extends between node 117 and the anode terminal
of the light emitting diode (LED) contained in a first
opto-isolator IC5. The cathode of the LED contained in the first
opto-isolator IC5 is connected to node 118. The opto-isolator
provides the electrical isolation between the telephone line
circuits and the control devices of the sensor circuit as required
by the regulations of the Federal Communications Commission.
The collector of the phototransistor contained in first
opto-isolator IC5 is connected to the positive voltage source. The
emitter of the phototransistor in the first opto-isolator IC5 is
coupled by a current limiting resistor R5 to the non-inverting
input terminal of comparator IC1. A third electrolytic capacitor C3
and a third resistor R3 couple the emitter of opto-isolator IC5's
transistor to ground.
Seventh and eighth resistors R7 and R8 are in series between system
ground and the positive voltage source to form a voltage divider.
The inverting input terminal of the first comparator IC1 is
connected to node 123 between the seventh and eighth resistors R7
and R8. The potential at node 123 serves as a reference potential
for the first comparator IC1.
The output terminal of the first comparator IC1 is coupled to the
base of a first NPN transistor Q1 by a current limiting resistor
R9. The collector of transistor Q1 is connected to the positive
voltage source. A current limiting resistor R11 and LED D10 are
connected in series between the emitter of transistor Q1 and
ground. The emitter of the first transistor Q1 is also connected to
one end of the coil of the second relay K2. The other end of the
coil 126 of relay K2 is directly connected to ground. A reverse
voltage clamping diode D8, which protects transistor Q1 from relay
coil voltage surges, is connected across the coil 126 of relay K2
with its anode connected to the end of the coil that is connected
to ground.
For the data device sensor circuit, the ring connector 133 is
connected to the negative terminal of a second electrolytic
capacitor C2 and to one alternating current input terminal of
bridge rectifier IC4. The other alternating current input terminal
of bridge rectifier IC4 connects to the positive terminal of second
electrolytic capacitor C2 and to the other terminal of the second
switch pole 110 of the second relay K2.
The positive output terminal of bridge rectifier IC4 connects to
node 119 and its negative output terminal is connected to node 120.
Three diodes D4, D5 and D6 are connected in a forward biased series
between nodes 119 and 120 to form a voltage clamping mechanism. A
second resistor R2 extends between node 119 and the anode of the
LED contained in a second opto-isolator IC6. The cathode connection
of the LED contained in the second opto-isolator IC6 is coupled to
node 120.
The collector of the phototransistor contained in a second
opto-isolator IC6 is connected to the positive voltage source. The
emitter of the phototransistor contained in second opto-isolator
IC6 is coupled by a sixth resistor R6 to the non-inverting input
terminal of a second voltage comparator IC2. A fourth electrolytic
capacitor C4 and a fourth resistor R4 couple the emitter of the
phototransistor in opto-isolator IC6 to ground.
The inverting input terminal of the second comparator IC2 is
connected to the reference potential at node 123. The output
terminal of the second comparator IC2 is coupled by a current
limiting resistor R10 to the base of a second NPN transistor Q2. A
current limiting resistor R12 is connected in series with an LED
D11 between the emitter of second transistor Q2 and ground. The
collector of the second transistor Q2 is connected to the positive
voltage source and its emitter is connected to one end of the coil
131 of the first relay K1. The other end of the coil 131 of first
relay K1 is connected to ground. A second reverse voltage clamping
diode D7 extends across the coil of first relay K1 which with its
anode connected to ground.
With reference to the FIGURE, there are a total of four pairs of
connections to the present device in its intended application. A
source of 12 volt direct current power is connected to terminals
101 and 102. A standard two-wire telephone line is connected to
connectors 103 and 104. A two-wire telephone line output connection
to a telephone system is provided by connectors 111 and 112. A
two-wire output connection to a data device is made to connectors
132 and 133.
A standard telephone line carries three types of electrical
signals. (1) The first signal is an alternating current which
carries the transmitted information, voice or data. The frequency
range of this information signal is typically from 50 to 4,000
Hertz, with a total power of one milli-watt or less. (2) The second
type of signal which is present in all normal operating modes of a
two-wire telephone line is an open circuit D.C. voltage typically
in the range of 15 to 52 volts. This voltage drops significantly
when a telephone instrument or data device goes "off hook" to use
the line. This voltage drop is detected by the switching equipment
supplying the voltage to determine when a telephone instrument or a
data device has gone "off hook" and seeks access to the telephone
line. 3) The third signal type is an alternating current ringing
signal in the range of 75 to 120 volts at 16 to 75 Hertz. This
voltage is used as a signal to devices on the telephone line to
become active and connect to the telephone line to accept incoming
voice or data transmissions.
When neither the telephone system or the data device is using the
telephone line, the switches of both relays K1 and K2 are in a
normally closed position as shown in the FIGURE. This couples the
tip connector 103 of the incoming telephone line to both the data
device tip connector 132 and the telephone system tip connector
111. The close state of relays K1 and K2 also couples the ring
connector 104 of the incoming telephone line through both sensor
circuits to the data device ring connector 133 and the phone system
ring connector 112. In this state when both the data device and
telephone system are "on hook", the current flowing through each of
the sensor's circuits is insufficient to turn on its respective
output transistor Q1 or Q2. Therefore, the coils of relays K1 and
K2 are in a de-energized state.
Then if the data device connected to terminals 132 and 33 becomes
active and creates a low off-hook resistive path between terminals
132 and 133, direct current will flow from telephone line tip
connector 103 through switch pole 107 of relay K2 to the data
device tip connector 132. A return current flows from the data
device ring connector 133 through the data device sensor circuit
and switch pole 110 to the telephone line ring connector 104.
Specifically, this direct current will flow through the bridge
rectifier IC4 which enables the control circuit 100 to operate even
if the tip and ring connections to the telephone line are
inadvertently reversed. In the case of such reversal, the current
flow through the sensor circuit will still be in the proper
direction to activate the circuit. As noted previously, the voltage
from the incoming telephone line across terminals 103 and 104 may
vary greatly from telephone line to telephone line. The series
connections of diodes D4, D5 and D6 provides a mechanism which
clamps this voltage to a fixed value independent of the current
flowing through the data device sensor circuit. The clamped voltage
that is across nodes 119 and 120 is applied across the series
connection of the LED in opto-isolator IC6 and the current limiting
resistor R2.
In this state, when the data device has seized the telephone line,
current flows through the LED in the second opto-isolator IC6. The
light from the LED in the second opto-isolator IC6 illuminates the
phototransistor contained within the opto-isolator to render the
phototransistor conductive. When the phototransistor becomes
conductive the 12 volts from the positive source is applied through
resistor R6 to the non-inverting input of second comparator IC2.
Previously this non-inverting input had been at ground potential
which produced a negative output from the comparator holding
transistor Q2 in an off or non-conductive state. When the
phototransistor in IC6 becomes conductive and applies the 12 volts
to the non-inverting input of IC2, the voltage at that input rises
above the reference voltage applied to the non-inverting input of
the second comparator IC2. This causes the output of the comparator
IC2 to rise to a potential near the 12 volt positive voltage
source. When this positive potential is applied to the base of NPN
transistor Q2 through current limiting resistor R10, the transistor
is turned on. When this occurs, the positive 12 volts is applied
across the coil of the first relay K1 which activates the relay
opening the DPST switch poles 106 and 109. This disconnects the
telephone system from the telephone line.
If, at this point, the telephone system becomes active and seeks
access to the telephone line, the disconnection by relay K1
prevents the telephone system from interfering with the existing
data communications on the telephone line from the data device.
When the data device becomes idle and goes into an on-hook state,
the resistance it presents across terminals 132 and 133 is
relatively high. This high resistance decreases the current flowing
through the data device sensor circuit deactivating it.
Specifically, either no current flows through the LED in
optoisolator IC6 or the current flow is so small that the LED is
not illuminated. This renders the phototransistor in IC6
non-conductive dropping the potential applied to the non-inverting
input of comparator IC2 to ground potential. As a result, the
potential at the output of the comparator IC2 drops to ground
potential turning off transistor Q2 and de-energizing the first
relay K1. The switch poles 106 and 109 of relay K1 thereby return
to their normally closed state coupling the tip and ring connectors
111 and 112 for the telephone system to the telephone line
connectors 103 and 104. This returns the operation of the control
circuit 100 to the state where both the data device connectors 132
and 133 and the telephone system connectors 111 and 112 are coupled
to the incoming telephone line connectors 103 and 104.
If both the telephone system and the data device have been idle and
then the telephone system becomes active, a low off-hook resistive
path is created between terminals 111 and 112. This low resistance
causes a direct current originating from telephone line tip
connector 103 to flow through switch 106 of relay K1 to the
telephone system tip connector 111. A return current flows from the
ring connector 112 through the telephone system sensor circuit and
switch pole 109 to the ring connector 104 of the telephone
line.
The current flowing through the telephone system sensor circuit
will activate its sensor circuit in the same manner as described
above with respect to the data device sensor circuit. Specifically,
the line current rectified by bridge IC3 will flow through the LED
of the first opto-isolator IC5 turning on its phototransistor. This
will apply a positive voltage to the non-inverting input of the
first comparator IC1 rendering its output positive. The positive
output from the comparator IC1 will turn on the first NPN
transistor Q1 activating the second relay K2 to open its DPST
switch. This disconnects the data device from the telephone line
connectors 103 and 104. In this state the telephone system has
accessed the telephone line and any activity by the data device
will not interfere with that connection. For example the data
device is prevented from accessing the telephone line and sending
data tones over the line while the telephone system has accessed
the telephone line.
The present control circuit 100 also prevents the ringing signal
applied by the telephone company over the telephone line from
activating either of the sensor circuits. Yet the ringing signal is
coupled to the data device and the telephone system. Specifically,
electrolytic capacitors C1 and C2 pass the alternating ringing
signals to the telephone system and the data device respectively.
Resistor R3 and capacitor C3 at the output of the opto-isolator IC5
and resistor R4 and capacitor C4 at the output of opto-isolator IC6
provide RC time constants in their respective sensor circuits.
These time constants prevent the ringing signal from turning on the
corresponding output transistor, Q1 or Q2. Specifically, the values
for these resistors and capacitors are selected so that the time
constant is approximately three times the period of the lowest
ringing signal frequency, about sixteen Hertz. Therefore, even
though the ringing signals when rectified by bridges IC3 and IC4
will momentarily cause the phototransistor in opto-isolators IC5
and IC6 to become conductive, the RC time constant prevents the
potential at the non-inverting inputs of the comparators IC1 and
IC2 from ever reaching a level above the potential at the inverting
inputs. Therefore, the output transistors Q1 and Q2 will never be
turned on by the ringing signal.
In the idle state, the present automatic telecommunication control
circuit 100 couples both the data device and the telephone system
to the incoming telephone line so that both may receive a ringing
signal that is transmitted over the telephone lines. The present
device also provides a mechanism for allowing the ringing signals
to be sent from the telephone line to both the data device and the
telephone system without activating the sensor circuits within the
control device 100. However, when either the data device or the
telephone system goes into an off-hook state, the other one is
disconnected from the telephone line. This prevents the other one
of the data device or the telephone system from interfering with
established communications on the telephone line. In addition, the
unique nature of the present control device 100 allows it to be
used with telephone systems having a wide range of signal
characteristics.
* * * * *